1. Field of the Invention
The present invention relates to a broadcast receiver such as a television receiver which receives a plurality of video/audio signals.
2. Description of the Related Art
Some television receivers have a picture-in-picture (PinP) function for displaying a main-picture (also referred to as a parent picture) and a sub-picture (also referred to as a child picture) simultaneously in a single image display screen. When the PinP function is used, the speaker usually outputs the sound of the main-picture and does not output the sound of the sub-picture. For example, the user (i.e., viewer) can view and enjoy a drama or a movie with sound in the main-picture while watching a program, the highlight scenes (such as a scoring scene) of which would be worthy of watching, such as a sports program, without sound output, and can switch between the main-picture and the sub-picture as necessary. With this type of use, however, the viewer must watch the main-picture while paying attention to the sub-picture without sound output and cannot devote himself or herself to enjoying the program shown in the main-picture. The viewer may miss a highlight scene broadcasted in the sub-picture when the viewer fails to notice the highlight scene.
There is one television receiver proposed to prevent this type of failure: The television receiver always monitors the audio output level of the sub-picture, determines that the scene is a highlight scene if the audio signal exceeds a predetermined level and if the audio signal exceeding the predetermined level continues for a predetermined period of time, records the video and sound of the determined highlight scene on a recording medium, and reproduces the program from the highlight detection time when the television viewer switches to the sub-picture. For example, refer to Japanese Patent Application Kokai (Laid-open) Publication No. 2003-134415 (Patent Document 1), page 6 and FIG. 1.
Further, there is another television receiver proposed with a function of monitoring the audio signal of a channel until the viewer changes the channel when a broadcast program is switched to a commercial break and returning the channel automatically to the channel selected before the change when the end of the commercial break is detected. For example, refer to Japanese Patent Application Kokai (Laid-open) Publication No. H5-199470 (Patent Document 2), page 5 and FIG. 5.
The television receiver of Patent Document 1 recognizes a highlight scene on the basis of the audio output level. It is, however, hard to specify an appropriate audio output threshold for recognizing a highlight scene, on the basis of the audio output level that depends largely on the broadcast station and program. A commercial break is often mistaken for a highlight scene because its audio output level is usually higher than that of an actual program.
Further, the television receiver of Patent Document 2 detects the end of a commercial break when the channel, in which the audio signal is monitored, is switched to a sound multiplex broadcast. The method to detect a commercial on the basis of the sound system can be applied only when the sound system of the actual program is a sound multiplex broadcast or a monaural broadcast and when the commercial is a stereo broadcast or a broadcast other than the sound multiplex broadcast.
Furthermore, in the television receiver of Patent Document 2, the system automatically switches the picture when it detects the end of a CM break. If the viewer does not want the automatic picture changeover, that is, if the viewer's interest has turned from the program before the change of the channel in which the end of a CM break has been monitored to the currently viewed program after the channel change, the viewer would find the automatic picture changeover embarrassing.